In an optical module, a RX_LOS signal (Loss Of Signal signal at receiver side) is an indication signal for indicating whether received optical power is lower than a preset threshold. In practical applications, a decision threshold of LOS alarm fixedly is fixedly set in a limiting amplifier of the optical module. Upon the optical module receiving an optical signal, the received optical signal will be processed by the trans-impedance amplifier (TIA), and the generated alternating current (AC) signal is inputted into the limiting amplifier. Then the limiting amplifier compares the amplitude of the AC signal with the preset LOS alarm decision threshold, and a comparison result is output to a processor as a RX_LOS signal, thus enabling the processor to determine whether to generate a LOS alarm based on the RX_LOS signal. Therefore, in the optical module, the setting of the LOS alarm decision threshold has a crucial effect on the decision of LOS alarm.
At present, the LOS alarm decision threshold is set as follows: after the arrangement of the photodetector APD, TIA and limiting amplifier, the LOS decision threshold is experimented by using several module samples and verified by using a small batch of modules. Then the LOS decision threshold will be adjusted according to the verification result and finally fixed.
However, due to different arrangements of APD, TIA, limiting amplifiers or different lengths of lines, the LOS alarm decision threshold of the limiting amplifier will be different, thereby causing a large amount of experimental data to be needed for determining the threshold level during use, so the use is inconvenient and of low efficiency.